Actuatable stop

ABSTRACT

An actuatable stop particularly suited for use as a &#39;&#39;&#39;&#39;dead man&#39;&#39;&#39;&#39; stop in arresting &#39;&#39;&#39;&#39;drift&#39;&#39;&#39;&#39; for cranes and the like, characterized by a rigid stop ring circumscribing an associated crane&#39;&#39;s pedestal and an actuatable locking mechanism including a reciprocating shaft adapted to extend from the pedestal into locking engagement with the ring in response to an actuation of an associated control, a feature of the stop being the inclusion of means for extending the shaft in response to a detected poweroff condition for the crane, whereby rotation of the pedestal automatically is arrested as the crane&#39;&#39;s power train is deactivated.

United States Patent Orendorff et al. 1 May 23, 1972 54] ACTUATABLE STOP3,456,810 7/1969 Ely ..212/39 Inventors: 1 we" C. orendorfi; Harvey L.Matter, 1,210,288 12/1916 Farr .....lO4/47 both of Fresno, Calif.FOREIGN PATENTS OR APPLICATIONS Assignw y Enterprises, 1,158,546 12/1963Germany ..104 47 22 'l d: 70 1 Fl e Jan 19 Primary Examiner-Harvey C.Hornsby [21] Appl. No.: 627 Attorney-Huebner & Worrel 57 ABSTRACT [52]US. Cl ..2l2/39, 104/47, 212/69 1 [51 1 Int. Cl. 1 ..B66c 13/48 Aactuatable p p r larly ited f r use as a dead man [58] Field of Search..212/39, 66-69; p in arresting for cranes and the like, Characterized104/35, 47; 174/526 527 by a rigid stop ring circumscribing anassociated cranes pedestal and an actuatable locking mechanism includinga [56] References Cited reciprocating shaft adapted to extend from thepedestal into locking engagement with the ring in response to anactuation UNITED STATES PATENTS of an associated control, a feature ofthe stop being the inclusion of means for extending the shaft inresponse to a detected Dechantsrelter p condition for the crane wherebyrotation of the 1,808,898 6/193] Kerr 212/69 pedestal automatically isarrested as the crane's power train is 3,249,336 5/1966 Brown 254/187 deactivated. 3,445,014 5/1969 Kullerback 214/77 3,447,692 6/1969 Thomas..212/39 1 Claim, 10 Drawing Figures PATENTEDmms I972 3,664,515

SPEET 1 OF 3 MAXWELL C. ORENDORFF HA/Pl/E) L. MATTERN INVENTORS ATTORNEVS PATENTEDmvza m2 3,664,515

sum 2 BF 3 MAXWfLL c. ORENDORFF HARVEY L. MA 7'7'ERN /N VE N T 0R3 ATTORNEVS PATENTEDMAY 23 I972 3.664.515

saw 3 BF 3 D 1 w fig l i L i L MAXWELL c. ORENDORFF O O (1 3 ,Q (L (1HARVEY L. MATTERN INVENTORY F610. 3 MWLM A TTORNEVS ACTUATABLE STOPBACKGROUND OF THE INVENTION The invention relates to "dead man stops andmore particularly to a dead man" stop particularly suited for employmentwith a boom-supporting pedestal of a crane and adapted to respond to ade-energization of the crane's drive train for effecting a locking ofthe pedestal against rotation.

The prior art is replete with braking mechanisms employed in arrestingthe translatory displacement of pivotally supported booms such as thoseemployed by cranes and the like. Among the mechanisms presently utilizedare mechanically actuated brake shoes, bands, dash-pots, and similarresponsive devices which serve to dissipate the kinetic energy of arotating boom. Another type of stop often employed is a rigid stopmounted adjacent to a cranes pedestal so that displacement of thepedestal is arrested as its displacement through a selected angle iscompleted for causing selected portions of the pedestal to engage thestops. I

One of the problems which continues to confront those involved in thedesign and use of cranes, particularly cranes of the type which aresupported on flatbed vehicles and the like, is the likelihood that theboom, when loaded, will tip" or capsize the supporting vehicle. Thisparticularly is true in those instances where the boom is displaced to aposition extending laterallv from the sides of the supporting vehicle.As is readily apparent to those familiar with the use of such cranes,the greater the length of the boom the greater is the tendency tocapsize, due to the length of the resulting moment arm.

However, it also is highly desirable to provide any given boom with aworking span or length sufficient to extend the distal end of the boomto selected points located at practical distances from the pedestalunder optimum load conditions. Where a boom is supported on a vehicle,such as a flatbed truck, the working radius is greater in fore-and-aftdirections, relative to the longitudinal axis of the supporting vehicle,than in lateral directions. This is due to the increased effectiveradius of the supporting structure in fore-and-aft directions.Consequently, precise control of the pedestals rotation must at alltimes be exercised in order to avoid drift and over-extension.Additionally, since the distal end of a boom normally is brought intoclose proximity with various types of structures such as buildings,power lines and the like, limits of displacement must be accuratelydetermined and fixed. In practice, drift and over-extension may resultfrom power failure at the braking mechanism and from other factors of asimilar nature which create conditions wherein a boom is not positivelydriven but is free-wheeling" and its rotation is unarrested.

OBJECTS AND SUMMARY OF THE INVENTION This invention overcomes theaforementioned difficulties by providing an actuatable stop,particularly suited for use with the boom-supporting pedestal of apower-driven crane, including a stop ring rigidly fixed to a supportingbase and circumscribing an actuatable locking mechanism adapted torespond'to a power-off condition for the cranes power train to achieve apositive coupling between the mechanism and the ring for thus couplingthe pedestal with the base whereby displacement therebetween .isarrested and boom drift is avoided.

Accordingly, an object of the invention is to provide an improvedselectively operable stop for use with a rotatable pedestal.

Another object is to provide a stop for arresting boom overtravel for avehicle supported crane.

Another object is to provide a stop particularly suited for use inarresting the rotation imposed on a vertically disposed boom-supportingpedestal in the presence of a power-off condition for the pedestalspower train.

Another object is to provide a stop for arresting the undesireddisplacement of the boom of a crane supported by an automotive vehicle.

Another object is to provide a dead man" stop for detecting theexistence of a power-off condition within the power train of a'rotatablv driven crane and responsively activating the stop to achieve apositive coupling between a base-supported stop ring and acrane-supported locking mechanism for thus limiting azimuthal rotationof the cranes boom in the presence of a detected power-off condition.

These, together with other objects, will become more fully apparent uponreference to the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary view of apower-driven crane, mounted on a flatbed vehicle, provided with anactuatable stop embodying the principles of the present invention.

FIG. 2 is a perspective view, on an enlarged scale, of the stop shown inFIG. I, particularly illustrating the operative relationship of the stopring and its associated actuatable locking mechanism.

FIG. 3 is a schematic view of a simplified electrical circuit asprovided for controlling the operation of the actuatable stop shown inFIGS. 1 and 2.

FIG. 4 is a top plan view of the locking mechanism, as shown in FIG. 2but with its cover plate having been removed.

FIG. 5 is a side elevation of the stop, taken generally along line 5-5in FIG. 4.

FIG. 6 is a partially sectioned end view of the stop illustrated inFIGS. 4 and 5.

FIG. 7 is a perspective view illustrating supporting structure employedin supporting the locking mechanism shown in FIGS. 4 through 6.

FIG. 8 is a partiall sectioned side elevation of a modified form of thestop illustrated in FIGS. 4 through 6.

FIG. 9 is a partially sectioned side elevation of still another modifiedform of the invention.

FIG. 10 is a detailed view of a circuit interrupter which may beemployed with the stop illustrated in FIGS. 1-9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Form Referring to FIG. 1,a stop 10, which embodies the principles of the present invention, isillustrated in an operative environment relative to a boom-supportingpedestal 12. As illustrated, the pedestal 12 may be supported on a bed14 provided for a flatbed truck, not designated. The pedestal 12 issupported for azimuthal rotation and serves operatively to support oneend of a boom 16. The particular configuration and type of the boom 16with whichthe stop 10 is employed is a matter of choice or convenience.However, it is to be understood that the boom 16 normally is anextendible boom which, in operation, is extended to predeterminedlengths whereby the booms distal end may be displaced to describepreselected arcs about the pedestal 12.

As a practical matter, the pedestal l2 selectively is driven in rotationby hydraulically or electrically activated power trains, includingsuitable gear trains 17 which impart selected rates of rotation to thepedestal. While not shown, it is to be understood that the pedestal 12also includes suitable bearing structure upon which is supported alaterall extended base plate 18 adapted to be driven in rotation withthe pedestal.

About the pedestal 12, in circumscribing relation to its base plate 18,there is disposed a stop ring 20, of a generally annular configuration,having a plurality of vertically extended teeth-like protrusions 22.These protrusions are spaced equidistantly about the uppermost surfaceof the ring 20 in a manner such as to define an annular row ofvertically extended teeth circumscribing the base plate 18.

In order to expedite the mounting of the ring 20 on the bed 14, the ringis divided into arcuate segments, designated 24 and 26, and is providedwith a plurality of radially extended mounting plates 28 having openings29 formed therein for accommodating a bolting of the independentsegments to the bed. Of course, as can readily be appreciated, the ring20 can be secured to the bed 14 in any suitable manner includingwelding, bolting, clamping or by any other suitable means which rigidlycouples the ring 20 with the bed 14, whereby the ring 20 is disposed inclose proximity with the peripheral surface of the base plate 18.

On the ring 20 there is mounted a pair of releasably coupled stops 30.Each of the stops 30 includes a pair of depending ears 31 disposed inmutual parallelism and adapted to receive therebetween the ring 20 inorder that the stop 30 may be seated on the upper surface of theprotrusions 22. The stops separately are secured in place through theuse of pins 32 extending through coaxially aligned openings 33, formedin the ears 31, and openings 34 extended radially through the ring 20 incoaxial alignment with the openings 33. Therefore, the stops 30 may beselectively positioned about the circumference of the ring 20 andsecured in place by inserting the pins 32 through the coaxially alignedopenings 33 and 34.

As illustrated in FIG. 2, the ring 20 is associated with an actuatablelocking mechanism, generally designated 40. The locking mechanism 40 issupported by a bracket 41 secured to depend from the peripheral surfaceof the base plate 18 by any suitable means, including welds 42. Withinthe bracket 41 there is a housing 43, which contains the mechanism 40,adapted to be displaced relative to the ring 20 as the boom 16azimuthally is displaced and the plate 18 is rotated for thus displacingthe bracket.

Within the housing 43, there is supported a plurality of actuators 44.In the first form of the invention, as illustrated in FIG. 3, theactuators 44 are electrically energizable solenoids, includingelectrically energizable coils 45. The coils are connected, throughsuitable leads 46, within a power train control circuit 47 and establisha magnetic field thereabout as a current flow is established in thecircuit. The circuit 47 serves to connect a suitable voltage source Vwith the cranes power train and brake assemblv 48 for driving thepedestal 12 in azimuthal rotation.

As depicted in the simplified diagram, the circuit 47 further includes amaster control switch 50 which is actuated to energize the power trainand brake assembly 48 in accordance with selected modes of operation. Asillustrated, the switch 50 is a simple on-off switch, however, as shouldreadily be apparent, the switch 50 is compatible with the specificcircuit employed and, where desired, may constitute a two-way switch forreversing the direction of current flow through the leads 46 of thecontrol should the source V include a DC source of electrical current.

Since the specific control switch 50 is in practice varied as founddesirable under given operative conditions, a detailed description isomitted. However, it is to be understood that the switch 50 serves tointerrupt the flow of current through the coils 45 as the switch isactuated to de-energize the power train 48 when termination of azimuthalrotation for the boom 16 is desired. Furthermore, it is to be understoodthat the specific circuitry employed in connecting the actuators 44 withthe power train control circuit 47 may be varied as desired, so long asthe flow of current through the coils 45 of the actuators 44 is dictatedthrough an actuation of switch 50 in order that the actuators 44 beactivated in response to changes initiated in the current flowingthrough the circuit 47.

As presently employed, each of the actuators 44 is provided with anoutput shaft 52 coaxially aligned and coupled with an armature 54 which,in turn, is magnetically coupled with the coils 45 in order that theshaft 52 may be reciprocated. Of course, the armature 54 and shaft 52may, if desired, be fabricated as a single shaft. Concentrically seatedabout the shaft 52 there is provided a compression spring 56 which isdisposed between a collar 58, rigidly fixed to the shaft 52, and aconcentric abutment plate 59.

Consequently, the shaft 52 is retracted toward the associated coil 45,in response to an electrical energization thereof, and is extended fromthe coils under the influence of the recovery forces of the spring 56,acting against the collar 58, when the coils 45 are electricallyde-energized Therefore,

as currently employed, the shaft 52 is reciprocated by opposing forcesapplied thereto by the coils 45 and the compression spring 56.

Since the coils 45 are connected in circuit series with the power trainand brake assembly 48, it can readily be appreciated that the shaft 52of each of the actuators is extended in the event the circuit betweenthe assembly 48 and the voltage source V is interrupted, without regardto the specific manner in which the circuit is interrupted. Furthermore,it also should be apparent that the shafts 52 of the actuators 44 areretracted upon a completion of an electrical path through the circuit 47for thus electrically energizing the coils 45. Therefore, the positionof the output shafts 52 for the actuators 44, at any given instant, isdictated by the state of energization of the circuit 47 as it isemployed to control the power train and brake assembly 48.

As best shown in FIGS. 4 and 5, the bracket 41, which supports themechanism 40, is of a generally rectangular configuration and includes apair of parallel, vertically disposed end plates 62 coupled togetherthrough a parallel pair of side plates 64. Each of the end plates 62 isprovided with a downwardly directed opening 66, FIGS. 2 and 6, whichreceives the teeth-like protrusions 22 of the ring 20, wherebv relativedisplacement therebetween is achieved as the base plate 18 is rotatedrelative to the ring 20.

The actuators 44 operatively are supported within the bracket 41 by areciprocably mounted support 70, FIG. 7, which forms a base for thehousing 43. The support 70 includes a laterally extended, rectangularbase plate 72, of rugged construction, having coplanar and parallelchannular tracks 74 extended along the parallel side edges of the plate.The tracks 74, as best shown in FIG. 6, are employed in coupling thebase plate 72 to the opposite side walls 64 of the bracket 41. It isintended that the support 70 be reciprocated relative to the bracket 41,therefore, the channular tracks 74 are coupled with the side plates 64of the bracket 41 through a pair of laterally extended coplanar rails76, which extend laterally from the opposite side walls of the lowerportion of the bracket 41. The rails 76, in practice, are insertedwithin the channels 74 in order that the plate 72 of the support 70 maybe displaced relative to the bracket 41.

The base plate 72, and the side plates 64 of the bracket 41 are sodimensioned as to permit the plate 72 to be reciprocated throughpre-selected distances relative to the end plates 62. However, in orderthat reciprocation imparted shock for the support 70 be dissipated, thebase plate 72 is provided with a pair of force dissipating compressionsprings 78 at each of its opposite ends. These springs are mounted incoaxiallv aligned openings 79, formed in the opposing surfaces of theend plates 62 and the ends of the base plate 72 and position the housing43 at an intermediate position between the plates 62. Therefore, it isto be understood that any reciprocation of the base plate 72 is achievedin opposition to the recovery forces of the compression springs 78whereby a shock absorbing function is performed by the springs as thehousings displacement is initiated.

In order that displacement of the actuators 44 may be supported withinthe bracket 41, the base plate 72 is provided with an upstanding wall 80which is welded in a vertical relationship with the upper surface of thebase plate 72. The wall 80 includes a plurality of openings 82 throughwhich suitable mounting screws 84 are extended for coupling thereto aretainer bracket 86. The bracket 86 is of any suitable design andcircumscribes the actuators 44 for maintaining them in a fixedrelationship relative to the plate 72. The plate 80 is furthersupported, at its opposite ends, by a pair of support walls 88 welded orotherwise fixed to the end portions of the plate 80 and to the baseplate 72 for thus imparting rigidity to the support 70.

The base plate 72 further is provided with a pair of vertically extendedopenings 90 arranged in coaxial alignment with the output shafts 52 ofthe actuators 44. Through each of the openings 90 there is extended alocking pin 92 coupled to the output shaft 52 through a convenientknuckle-pin coupling 94. As illustrated in FIGS. 5 and 6, a distal endof each of the pins 92 is received in spaces formed between theteeth-like protrusions 22 and acts as a locking pawl. The knuckle-pincouplings 94 permit the distal ends of the pins 92 to be deflected fromcoaxial alignment with the shafts 52 in order that they may be insertedinto a locking engagement with the ring 20, without prior alignmentbeing accurately achieved between the protrusions and the pins.

Consequently, when the power train and brake assembly 48 are activated,through a selected closing of the switch 50, the coils 45 of theactuators 44 serve to retract the shafts 52 upwardly and out ofengagement with the protrusions 22. Consequently, as the pedestal 12 isdriven in rotation through a selective activation of the power train andbrake assembly 48, the pins 92 are displaced relative to the ring 20.However, when the switch 50 is actuated for interrupting the electricalcircuit to the power train and brake assembly 48, for thus deenergizingthe drive train and actuating the brake assembly, the compressionsprings 56, acting against the collars 58, drive the locking pins 92downwardly causing the distal ends to act as locking pawls to becomemated with the protrusion 22 for establishing a fixed couplingtherebetween. Since the distal ends of the pins 92 are fixed relative tothe ring and the bracket 41 is fixed to the base plate 18 of thepedestal 12, a displacement between the base plate 18 and the ring 20 islimited through the snubbing" effect of the springs 78. in the event thebrake of the brake assembly malfunctions, or otherwise fails to arrestrotation of the pedestal 12, the rigidly coupled locking mechanism 40and the stop ring 20 serve to arrest rotation of the pedestal 12, andconsequently limit the travel of the boom 16. When the master controlswitch 50 is again actuated, so that current flow from the voltagesource V to the power train and brake assembly 48 is initiated, thecoils 45 again are actuated for retracting the distal ends of the pins92 from between the protrusions 22 of the ring 20, whereby displacementbetween the locking mechanism 40 and the stop ring 20 again isaccommodated.

As best illustrated in FIG. 5, it will be noted that the actuators arepaired and so spaced that when the end portion of one of the pins 92 isseated between a pair of the protrusions 22, the locking pin 92 of theother actuator of the pair is engaged by the uppermost surface of one ofthe protrusions 22. Consequently, the pins 92 are spaced within thebracket 41, relative to the teeth-like protrusions 22, so that once thecircuit through the coils 45 is interrupted the maximum displacementwhich can occur between the ring 20 and the bracket 41, before seatingof the distal end of one of the pins 92 occurs, is limited to thediameter of one of the pins. Therefore, for all practical purposes, thecoupling achieved between the locking mechanism 40 and the stop ring 20is simultaneous with an interruption of the power circuit.

Second Form Turning to FIG. 8, therein is illustrated another form ofthe invention. As depicted, the actuators 44 comprise hydraulic or,alternatively, pneumatic actuators 100 coupled to a suitable source ofpressurized fluid, not shown, for axiallv driving the pins 92 againstthe applied force of the springs 56 in order to retract the distal endsof the pins 92 from the spaces arranged between the teeth-likeprotrusions 22 of the ring 20.

As a practical matter, the actuators 100 are quite similar in design andfunction to the actuators 44, previously described. However, in lieu ofelectrically energizable coils 45, each of the actuators 100 is providedwith a piston including a pressure driven piston head 102 receivedwithin a pressure cylinder 104 and mounted on an extended shaft 105 towhich is coupled a pin 92. The cylinder is pressurized as pressure isdelivered thereto through an inlet port 106 coupled to the source offluid through a suitable fluid conduit 108, while the conduit 108 actsas a pressure line for delivering fluid under pressure to the cylinder104, it also serves as a relief line for relieving the pressure withinthe cylinder.

When it is found desirable, because of the weight and strengthrequirements imposed by the kinetic energy imparted to the boom 16 andits pedestal 12, the pins 92 simultaneously are extended and coupledwith the ring 20. To achieve this, the actuators laterally are spaced atdistances such that the depending pins 92 are spaced in acenter-to-center relationship with the openings formed between theprotrusions 22 in order that the pins 92 of the actuators 100 may beseated in a coupled relationship with the ring 20 as the springs 56 actto extend the shafts as the cylinders 104 are de-pressurized.

Pressurization control for the cylinders 104 is achieved through apressure system of a suitable design. Since such systems are readilyavailable, a detailed description thereof is omitted in the interest ofbrevity. However, it is to be understood that the system includes asuitable selector valve, also not shown, associated with the switch 50and operatively is driven in a manner such that as the switch is closed,for energizing the circuit 47, the selector valve is actuated forpressurizing the cylinder 104, through the line 108, whereupon thepiston head 102 within each actuator is displaced for retracting theassociated pin 92 in a manner consistent with that hereinbeforedescribed with regard to the actuators 44. Likewise, de-pressurizationof the cylinder 104 occurs as the circuit 47 is interrupted, whereuponthe pins 92 are displaced into a coupled relationship with the ring 20by the applied force ofsprings 56.

Third Form A further embodiment 40 of the instant invention isillustrated in FIG. 9 which is quite similar in design and function tothat hereinbefore described. However, the distal end of a single pin 92is connected with a plate from which depends a plurality of aligned andequally spaced teeth or pawls 112. The pawls 112 are on acenter-to-center spacing with the protrusions 22 of the ring 20. Thepawls 1 12 may be connected with actuators 44 or 100, as desired.Consequently, when the actuator-associated locking pin 92 is extended,through an actuation of the actuator or control, the plurality of pawls112 are seated between the plurality of protrusions 22 of the ring 20for thus achieving a desired locking relationship therebetween. Thisseating of the pawls 112 serves to effect an interlocking of the lockingmechanism 40 and the ring 20.

Circuit Interrupter As illustrated in FIG. 10, the locking mechanism 40may be provided with a circuit interrupter 115. The interrupter includesa spring-loaded, axially reciprocable rod having a laterally extendedfoot 121 so disposed as to engage the vertical face of a stop 30 as thelocking mechanism is displaced about the circumference of the ring 20.

Within the bracket 41 of the locking mechanism 40 there is mounted amicroswitch 122 which is biased to an open condition, but which normallyis closed through a spring-loaded actuator arm 124 depressed forpurposes of closing the microswitch. As a practical matter, switch 122is coupled within the circuit 47 in circuit series with the voltagesource V and the locking mechanism 40 in a manner such that the circuit47, between the voltage source V and the locking mechanism 40 isinterrupted through a circuit-opening actuation of the microswitch.

In order to maintain a closed current path through the microswitch 122,the rod 120 is mounted for reciprocation within a concentric sleeve 126and is spring-biased to an extended disposition by a concentriccompression spring 128. At the innermost end of the rod 120 there isprovided a switchactuating cam which engages the arm 124, when the rod120 is fully extended, to maintain the switch 122 in a closed position.However, when the locking mechanism 40 is displaced toward the stop 30sufficiently for causing the foot 121 to engage the face of the stop 30,the rod 120 is retracted against the applied force of the spring 128sufficiently for unseating the cam 130, with respect to the actuator124, whereupon the circuit 47 is opened between the voltage source V andthe locking mechanism 40 whereby the stop 10 is rendered effective forarresting displacement of the pedestal 12 in the manner hereinbeforedescribed.

In those instances wherein the microswitch 122 is employed, it isimportant to note that the circuit 47 must be provided with a by-passswitch 132, FIG. 3, which preferably is a normally open switch, adaptedto be actuated to a closed condition in order that a circuit path may becompleted through the switch 50 so that the power train and brakeassembly 48 may again be actuated and the pedestal 12 driven in areverse direction for causing the boom 16 to reverse its direction oftravel a distance sufficient to permit the arm 124 to again be extended.The specific configuration of the by-pass switch 132 is a matter ofconvenience and may be varied as found practical.

OPERATION OF THE PREFERRED EMBODIMENTS The operation of the describedembodiments of the subject invention is believed to be readily apparentbut is briefly summarized at this point. As the operation of the lockingmechanism 40 is similar for the various forms of the inventionhereinbefore described, it is believed that a single description of theoperation of the dead man stop 10 will suffice to provide a completeunderstanding of the present invention.

As best illustrated in FIG. 1, the boom 16 is driven in azimuthalrotation in response to a selective energization of the power train andbrake assembly 48. In the event it is desirable to arrest rotation ofthe boom 16, the power train and brake assembly 48 selectively isde-energized through a switching of the switch 50, FIG. 3. As thisswitching occurs, the circuit through the coils 45 of the actuators 44simultaneously are de-energized, whereupon the output shafts 52 of theactuators are caused to descend, under the influence of the springs 56,for thereby causing the distal ends of the pins 92 to act as pawls andseat between the vertically disposed protrusions 22.

In instances where the actuators 100 are employed and activated throughdelivery of fluid under pressure to the actuator, as illustrated in FIG.8, the circuit shown in FIG. 3, also activates a solenoid, not shown,which serves to actuate a selector valve, also not shown, so that aspressure within actuator 100 is relieved the springs 56 are renderedeffective for seating the distal ends of the shafts relative to the ring20 for thus establishing a coupling therebetween.

In the same manner, the depending teeth 112 of the plate 110 are seatedrelative to the stop ring 20 in response to an actuation of anassociated actuator.

In any event, once the variously emplo ed actuators 44 and 100 arecaused to be actuated, the locking mechanism 40 is coupled with the ring20 through an extension of the pins 92, or 112, as the case may be, withthe teeth-like protrusions 22. However, additional travel for the boom16 is accommodated through the springs 78 for achieving ashock-absorbing or snubbing effect for the locking mechanism 40 as theplate 72 is displaced along the rails 76 against the applied forces ofthe springs 78.

When the pedestal 12 is to be rotated in a reverse direction, the switch50 again is actuated so that a current flow again is established betweenthe voltage source V and the power train and brake assembly 48,whereupon the distal ends of the pins 92, or pawls 112, are extractedfrom between the teeth-like protrusions 22 of the ring 20 in order thatdisplacement between the locking mechanism 40 and the stop ring 20 againis accommodated.

Where the stop 40 is provided with the circuit interrupter 1 forpurposes of assuring that over-travel and drift will not occur,regardless of the state of energization of the power train and brakeassembly 48, the foot 121 will engage the face of the stop 30 as thepedestal 12 is rotated for thereby causing the rod to be retracted asthe boom 16 is rotated. Retraction of the rod 120 serves to displace thecam 130, whereupon the spring-biased arm 124 is permitted to be elevatedfor there y opening the switch 122 and achieving an interruption of thecircuit 47. As the circuit 47 is interrupted, the associated actuatorsare rendered efiective for causing the locking mechanism 40 to arrestrotation of the pedestal 12. The circuit may again be closed, at theinterrupter 115, by closing the switch 122 or the switch 132, as foundpractical.

It should be apparent that the various actuators, type of locking pin orpawl employed, as well as the spacing of the protrusions for the stopring may be interchanged as found desirable and that the interrupter maybe employed with the variously described locking mechanisms.

In view of the foregoing, it is to be understood that the presentinvention provides a highly reliable, actuatable switch which serves asa dead man stop to arrest undesired rotation of a crane-associatedpedestal, whereby drift of the cranes boom is avoided.

Although the invention has been herein shown and described in what areconceived to be the most practical and preferred embodiments, it isrecognized that departures may be made therefrom within the scope of theinvention.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A stop for use with a crane having a rotatable pedestal mounted on arigid base and driven in rotation by electrically powered meanscomprising:

A. a stop ring circumscribing the pedestal and rigidly mounted on saidbase,

1. said ring being disposed concentrically of the rotatable pedestal andhaving upwardly disposed teeth of predetermined width measuredcircumferentially of the ring separated by interstices of substantiallythe same width; a pair of stops selectively positionable about thecircumference of said ring B. locking means including,

1. a bracket mounted on said pedestal in spaced relation to the stopring,

2. a pair of pins mounted in the bracket above the stop ring and injuxtaposition thereto for reciprocal elevational movement to and fromring engagement,

a. the pins being adapted to be received by the interstices and b.having centers spaced a distance equal to an odd numbered multiple ofthe tooth width whereby when one pin is aligned with a tooth the otherregisters with an interstice,

3. resilient means urging the pins downwardly into ring engagement, and

4. electromagnetic means individual to the pins adapted when energizedto retract their respective pins upwardly from the ring in opposition tothe resilient means; and

C. an electric circuit for supplying electrical energy to theelectrically powered means and simultaneously to the electromagneticmeans whereby the pins are retracted whenever the powered means inenergized,

1. said circuit including a switch having actuating means engageablewith said stops when said pedestal has been rotated through apredetermined rotation for simultaneously interrupting energization ofthe powered means and the electromagnetic means for release of the pinsfor receipt of one thereof into an interstice upon de-energization ofthe powered means.

1. A stop for use with a crane having a rotatable pedestal mounted on arigid base and driven in rotation by electrically powered meanscomprising: A. a stop ring circumscribing the pedestal and rigidlymounted on said base,
 1. said ring being disposed concentrically of therotatable pedestal and having upwardly disposed teeth of predeterminedwidth measured circumferentially of the ring separated by interstices ofsubstantially the saMe width; a pair of stops selectively positionableabout the circumference of said ring B. locking means including,
 1. abracket mounted on said pedestal in spaced relation to the stop ring, 2.a pair of pins mounted in the bracket above the stop ring and injuxtaposition thereto for reciprocal elevational movement to and fromring engagement, a. the pins being adapted to be received by theinterstices and b. having centers spaced a distance equal to an oddnumbered multiple of the tooth width whereby when one pin is alignedwith a tooth the other registers with an interstice,
 3. resilient meansurging the pins downwardly into ring engagement, and
 4. electromagneticmeans individual to the pins adapted when energized to retract theirrespective pins upwardly from the ring in opposition to the resilientmeans; and C. an electric circuit for supplying electrical energy to theelectrically powered means and simultaneously to the electromagneticmeans whereby the pins are retracted whenever the powered means inenergized,
 1. said circuit including a switch having actuating meansengageable with said stops when said pedestal has been rotated through apredetermined rotation for simultaneously interrupting energization ofthe powered means and the electromagnetic means for release of the pinsfor receipt of one thereof into an interstice upon de-energization ofthe powered means.
 2. a pair of pins mounted in the bracket above thestop ring and in juxtaposition thereto for reciprocal elevationalmovement to and from ring engagement, a. the pins being adapted to bereceived by the interstices and b. having centers spaced a distanceequal to an odd numbered multiple of the tooth width whereby when onepin is aligned with a tooth the other registers with an interstice, 3.resilient means urging the pins downwardly into ring engagement, and 4.electromagnetic means individual to the pins adapted when energized toretract their respective pins upwardly from the ring in opposition tothe resilient means; and C. an electric circuit for supplying electricalenergy to the electrically powered means and simultaneously to theelectromagnetic means whereby the pins are retracted whenever thepowered means in energized,